Method of heat treating hot rolled steel rods



July 24, 1956 J. H. CORSON ET AL METHOD OF HEAT TREATING HOT ROLLEDSTEEL RODS 2 Sheets-Sheet 1 Filed 001;. 19, 1950 NZS R 0 T l E mm N No MC T W A T Y A 2 m E JGAW July 24, 1956 J. H. CORSON ET AL 2,756,169

METHOD OF HEAT TREATING HOT ROLLED STEEL RODS Filed Oct. 19. 1950 2sheets-sheet 2 l\ 3?. I400 m E I200 KW TIME IN SECONDS INVENTOR Jomv HCoRsoN y 650m: A Goerz DARTREY LEWIS United States Patent C) METHOD OFHEAT TREATING HOT ROLLED STEEL RODS John H. Corson, Williamsport, andGeorge A. Goetz,

Morrisville, Pa., and Dartrey Lewis, Trenton, N. J., assignors, by mesneassignments, to John A. Roeblings Sons Corporation, Trenton, N. J., acorporation of Delaware Application October 19, 1950, Serial No. 190,9544 Claims. (Cl. 148-21.55)

This invention has to do with hot rolling and heat treating carbon steelrods to make them suitable for being drawn into wire.

In the production of steel wire it is customary to reduce the steelingots by hot rolling, first to billets and then to rods of the desiredsize such as 7 or diameter. The rolled rods are then heat treated as aseparate operation to perform what is known as patenting. This is a heattreatment which produces a metallurgical structure in the rod that makesit especially suitable for wire drawing. Such patenting involves passingthe rod very slowly through a furnace in which it is reheated to atemperature of l5501850 F. The rod as it emerges from the furnace isallowed either to cool naturally in the air, which is known as airpatenting, or is quenched in a bath of molten lead usually within thetemperature range 900-l300 F.

Most of the steel rods subjected to this treatment are of a plain carbonsteel composition in which the carbon content ranges usually from around0.20 to 0.95%. Rods of such composition as hot rolled contain a verycoarse structure of pearlite which is of irregular formation and makesthe rods unsuitable for cold wire drawing, except to a very limitedextent. The patenting operation improves this structure by first gettingthe carbon back into solid solution in the iron and then allowing thecarbon to come back out of solution in the form of very fine plates ofiron carbide (cementite) closely spaced. In fact the pearlitic structurethus obtained is frequently so fine that it cannot be readily resolvedunder the microscope even at 1000 magnifications. Such a structure hasmuch higher strength and is suitable for cold drawing through six ormore successive dies until the total reduction of area is 90% or more ofthe original cross-sectional area.

It will be apparent that it would be highly advantageous if the hotrolling and patenting process could be combined to avoid the necessityfor reheating the rods and the necessity for all the separate handlingoperations necessarily involved in the foregoing procedure. This hasbeen extremely difiicult to do, heretofore, because of the highfinishing speeds which are used in hot rolling the rods, and the factthat the time-temperature regulation needed in the patenting operationwhich is carried out at very slow speeds is not adaptable to such highfinishing speeds. For example, it is general practice in hot rollingrods to roll them in a continuous mill from a 2" x 2" billet through asuccession of reducing rolls to a rod that may be any- 1 where from to/8" in diameter. In such a rolling operation the rod is elongated eachtime its cross section is reduced, and it is customary for the rods toemerge from the last pair of rolls in such a mill at a speed of from2000 to 5000 F. R. M. Patenting operations, on the other hand, areusually carried out at much lower speeds, ranging from 10 to 100 F. P.M.

Finishing temperatures in a hot rolling mill are frequently of the orderof 1800 F., and in order to develop a metallurgical structure in :thisrodsimilar to that pro- "ice duced by patenting, it is necessary to coolit rapidly and uniformly from such a temperature to a temperature withinthe 9001300 F. range and then hold the rod within that range for aperiod of 10 seconds or more while the carbon comes out of solution. Ifthe rod is not cooled sufliciently the pearlitic structure will be toocoarse, especially in the center of the rod. If the rod is cooled toomuch, the center of the rod may be of the proper fine pearliticstructure, but the surface will be acicular o1 Bainitic in structure. Infact if the cooling is too great, definite hardening may be producedwith the formation of sorbite, rnartensite or similar structures whichgreatly impair the ability of the rods to be drawn.

An object of this invention is to provide a method and apparatus forquickly and uniformly cooling a rapidly moving rod from a temperature ofthe order of 1800 F. to a temperature within the range of 9001300 F.without cooling the outer portion of the rod substantially below 900 F.

Another object of the invention is to provide a method and apparatus foraccomplishing such rapid cooling and immediately thereafter holding therod within this temperature range for a sufiicient period of time topermit the carbon to separate from the solid solution in the form offine pearlite.

Another object of this invention is to provide a method and apparatusfor patenting plain carbon steel rods which can be carried out while therods are moving at very high speeds and which can be readily combinedwith the hot rolling of such rods on a continuous mill.

These and other objects of the invention will be apparent or explainedin connection with the following description of the invention and theaccompanying drawings in which- Figures 1 and 1A together illustratesomewhat diagrammatically apparatus for heat treating in accordance withthis invention steel rods as they come from a conventional mill for thecontinuous hot rolling of such rods.

Figure 2 is a vertical longitudinal sectional view showing on a largerscale one of the quenching units appearing in Figures 1 and 1A.

Figure 3 is a vertical longitudinal sectional view showing on a largerscale one of the liquid separating units appearing in Figures 1 and 1A.

Figure 4 is a cooling curve indicating the manner and rate at which therods are cooled in accordance with this invention.

It has been found that a fine grain pearlite structure can be obtainedby heat treating hot rolled rods as they emerge from the rolling mill ifthe rods are rapidly cooled to a temperature within the range of 9001300F. without cooling the surface of the rods at any time below atemperature of about 900 F., and are then held within the 900-1300 F.temperature range for 10 seconds or more until the carbon is all out ofsolution. By rapid cooling is meant cooling in a space of time of theorder of .75 to 1.5 seconds. Of course, if the cooling is too rapid itwill be virtually impossible to avoid cooling the outer surface of therods below 900 F. and, on the other hand, if the cooling is not rapidenough the pearlitic structure will be toocoarse.

Preferably, the rapid cooling to the temperature range of 900-1300 F.takes place between the time that the rod emerges from the last pair ofrolls in the rolling mill and the time that it is delivered to a reel orotherwise formed into a coil. If the rod is cooled to the propertemperature when it is formed into a coil, the mass of steel in the coilwill retain the temperature of the metal at the recalescence point for anumber of seconds, or at least long enough to permit all of the carbonto come out of solution in the form of fine pearlite.

It has been found that this rapid reduction of temperature without toodrestic coolingof the outer surface of the rod can be effectedsatisfactorily by subjecting the hot rod, as it comes from the rollingmill and while it is traveling at a .high rate of speed, .to successivealternate stages .of liquid quenching and air cooling. While otherliquids might be used for quenching, water is readily available .andserves the purpose very well. It is desirable to. avoid cooling theouter surface of the rod substautially below 9.00 F. and this isaccomplished by shortening the time of each water quenching stage as theoverall temperature of the rod is reduced. In other words, as the rodmoves along at a constant speed, the successive quenching units applywater to the surface of the rod for a shorter time.

.One form of apparatus suitable for carrying out heat treatment of steelrods as they issue from a hot rolling mill isillustrated somewhatdiagrammatically in the drawings. Figures 1 and 1A, when arranged intandem, indicate the complete apparatus for performing this heattreatment. The rod, indicated generally at 10, issues from between the.last pair of rolls 11, 11 of a conventional or other suitablecontinuous hot rolling mill at a temperature .of the order of 1800 F.This hot rod, traveling at a high rate of speed, immediately passesthrough a water quenching unit 12 and then in succession through a waterseparating or draining unit 13, an air cooling tube 14, a second waterquenching unit 15, water separating device 16 and air cooling tube 17 toa pair of pinch rolls 18,18. The pinch rolls 18,, 18 are driven andserve to keep the red hot rod moving smoothly. through the apparatuswithout cobbling. If the pathof travel for the rod after it leaves thelast pair of rolls of the rolling mill and before it reaches the take-upor coiling reel is not too, long, this intermediate pair of pinch rolls18, 18, may be omitted. On the other hand, if the path of travel isunusually long, it may be desirable to use more than one pair of suchdriven pinch rolls.

After the pinch rolls 18, 1.8, the rod is passed successively throughanother water quenching unit. 19, a 'Water separating unit 20, an aircooling tube 21, a fourth water quenching unit 22, followed by anotherwater separating unit 23 and an air cooling. tube 24. Tube .24 ispreferably curved to deliver the hot rod onto a reel, indicatedgenerally at 25. Such a reel orcoiling device mavbeof any conventionalor other design and, if desired, may be positively rotated by a ringgear 26 driven by a pinion 27.

The reel 25, may also be provided with a conventional stripper plate28which ,is elevated when a coil of rod is completed to a position levelwith the conveyor table .29. A ram,30 of any. suitable construction maybe provided to push the finished coil from the stripper plate 28 ontothe table 29, whence it is carried away by the conveyor 31. The finishedcoil is indicated at 32. in a position which, it occupies while beingcarried away by the conveyor 31.

Figure 2 illustrates in somewhat more detail one. suitable form for thewater quenching devices shown in Figures 1 and 1A at 12, 15, Hand 22.Essentially, such a unit may consist of a central tubular member 33having a flared forward end 34 and a number ofholes or perforations,indicated generally at 35. The tubular member is surrounded by a jacket36 which issupplied with water or other suitable quenching fluid underpressure through the pipe 37. The quenching fluid; is thus sprayedunder. pressure against the outer surface of. the rapidly traveling rod10, as, it moves through the'quenching unit. The heat of t the rodconverts some of this water or quenching fluid to vapor and the excessliquid spillsout from the ends of the tube 33 into a. trough or. othersuitable collecting basin, (not shown).

Because the rod. is moving so rapidly it is particularly. desirable toprovide further opportunity for. excess water to drain off its surface.This maybe done in a water separating, unit. such as shownat 13, 16, 20

and 23. One suitable form for such a unit is shown in Figure 3 andconsists essentially of a number of short tubular sections 40 spacedfrom each other along the path of travel of the rod. Each tubularsection preferably has a flared forward end to receive the travelingrod. These tube sections may all be held in proper alinement by means ofa metal bracket such as indicated at 42. Any excess water or otherquenching fluid carried along by the rod from the preceding quenchingunit is allowed to drain 01f before the rod passes into one of the aircooling tubes 14, 17, 21 or 24.

It will be noted that while the water separating units and the aircooling tubes are all substantially alike both in structure and size,the quenching units differ in length. For example, the second quenchingunit 15 is much shorter in length than the first quenching unit 12. Thethird quenching unit 19 is in turn substantially shorter than the secondunit 15, and the fourth quenching unit 22, if needed, may be madesmaller than the third one or it may be made approximately the same sizeas the unit 19. The purpose of making these quenching units ofsuccessively shorter lengths can best be explained in connection withthe following example.

Example..It may be assumed for purposes of this example that the rod tobe heat treated is a plain carbon steel rod A in diameter and is issuingat a temperature of 1800 F. from the last pair of rolls on aconventional Morgan continuous rod mill with a finishing speed of 4100F. P. M. (68.3 F. P. S.). It has been found that, the ideal treatment isto cool this rod to a uniform temperature of about 1100 F. as rapidly aspossible without subjecting the skin or any other portion of the rod to.a temperature less than about 900 F. during the cooling. When such a rodis passed through the machine of the type illustrated in Figures 1 and1A, the cooling eflect on the rod may be that indicated generallyv inthe graph of Figure 4.

The temperature is plotted against time so that this graphv showstherate of change of temperature as the rod moves along. The line 45indicates the temperature of the center of therod as it moves along,while the line 46 indicates the temperature of the outer surface of therod. As the rod. moves into and through the first quenching unit 12which, for purposes of illustration, may be 3.8 long, the outer surfaceof the rod is cooled to approximately. 1000 F. in .056. second. Thecenter of the rod, however, is cooled only slightly, as shown by thefirst small, dipin the line 45.0f Figure 4, and the rod then passesthrough the, units 13 and 14 which take up a total of 17.1 of travel.During this, time, which is approximately. 0.25 second, an equalizationof temperature between the outer surface and center of the rod takesplace, so that the outer surface of the rod rises rapidly to atemperature above 1400 F., while the temperature of the center of therod is cooled down to a temperature of a little less than 1500" F.Before the temperatures of the outer surface and center of. the rod-havecompletely equalized however, the rod passes through the secondquenching unit 15 which is 1.4 in length and rapidly cools the. exteriorof the rodto 1000 F. in .02 second. This is indicated at 46b inFigure 4.The center of the rod again is only, slightly cooled during thisinterval but during passage through the succeeding air cooling sections16 and 17, which takes up to a distance of 17.1 of travel, thetemperature of the outer surface of the rod risesrapidly to just, belowl300 F. while the center of the rod is cooled down to around 1300 F.

At this point the rod passes through the third quenching unit, 19 whichis 0.7' in length and in the space of .01 second coolsthe outer surfaceof the rod down to a little less than 1000? F., as shown bythe section460 of the curve 46 on the graph. Thereupon. another equalization takesplacewhiletherod is passing through the air cooling sections 20 and 2-1for a travel'of: 17.1, the temperature this time being equalizedaroundl1509 F. The

fourth quenching unit 22, which is also .7' long, then cools the outersurface of the rod down to around 900 F. in the space of .01 second asshown at 46a. The final equalization of the rod which takes place duringanother 17.1 of travel through the units 23 and 24 results in a rodwhich is delivered to the reel 25 at a substantially uniform temperaturethroughout this section, that temperature being 1100 F. or a littleless.

This whole operation, therefore, in a total time of 1.096 seconds andduring a total travel of 75 has reduced the temperature of the rod from1800 F. to a little below 1100 F. without any time cooling the outersurface or any part of the rod to a temperature below 900 F. which mightproduce the formation of the objectionable Bainite or martensitestructure.

As the rod is being wound up on the reel 25 and even after the completecoil of rod is being carried away by the conveyor 31, it is aflfordedample time at the proper temperature i. e. within the range of 900-1300"F. for all of the carbon in solution to come out in the form of a veryfine structure of pearlite. It will be apparent of course that theparticular conditions and dimensions will necessarily be varied in thetreatment of hot rolled rods of other sizes or of the same or othersizes which may be traveling at different speeds than the speed in theexample given. Also, adjustment of course will have to be made for rodswhich emerge from the rolling mill at a temperature that may be a littleabove or somewhat below 1800 F.

The terms and expressions employed are used as terms of description andnot of limitation, and it is not intended, in the use of such terms andexpressions, of excluding any equivalents of the features shown anddescribed or portions thereof, but it is recognized that variousmodifications are possible within the scope of the invention claimed.

We claim:

1. A method of heat treating hot rolled high carbon steel rods as thehot rod travels from the rolls to a coiling device at a temperature ofthe order of 1800 F. and at a speed of the order of 2000 F. P. M. ormore which comprises water quenching the rod and immediately removingsurplus water from the rod'surface, allowing the temperature of theouter and inner portions of the rod to equalize substantially, thenagain water quenching the rod and removing surplus water from the rodsurface, again allowing the temperature of the portions of the rod toequalize substantially, and repeating said treatments successively untilthe average temperature of the rod is reduced to a temperature of theorder of 1100 F. at the time it is coiled, each of said water quenchingtreatments being of short enough duration so that the outside surface ofthe rod is not cooled to a temperature substantially below 900 F. beforethe rod is coiled.

2. A method of producing high carbon steel rods suitable for wiredrawing without further heat treatment which comprises hot rollingbillets to rods, quickly cooling the rapidly traveling rod coming fromthe rolling operation at a temperature of the order of 1800 F. bysubjecting the rod as it travels along to a series of alternate waterquenchings and air coolings until the average rod temperature is reducedto a temperature substantially below 1300 F. but not below 900 F., andthen coiling the rod to retard further cooling while the carbon comesout of solution, each of said water quenchings being of short enoughduration to avoid cooling the surface of the rod substantially below 900F., and each of said air coolings being long enough to permitsubstantial equalizing of the temperatures of the inner and outerportions of the rod before the next water quenching treatment isapplied.

3. In a method of preparing steel rods for wire drawing by heat treatinga rod as it leaves a hot rolling mill at a temperature of the order of1800 F., the step of cooling the rod rapidly and relatively uniformly toa temperature within the range of 900-1300 F. by successively andalternately applying a quenching liquid to the rod and immediatelyremoving surplus liquid to allow the rod to equalize substantially intemperature as it moves along in a longitudinal direction, thesucceeding quenching treatments being of shorter duration than the firstquenching treatment to minimize overcooling of the surface of the rod.

4. -A method of heat treating hot rolled steel rod as the hot rodtravels at high speed in an axial direction from the finishing rolls ofa hot rod mill to a coiling device which comprises lowering the surfacetemperature of the rod to a greater degree than its interior temperatureby means of a brief water quench, immediately removing the water fromthe surface of the rod for a sufficient time for the surface temperatureof the rod to rise substantially during equalization of the temperaturewithin the rod,

and repeating said quenching and equalizing treatments in rapidsuccession until the average temperature of the rod is reduced fromaround 1800 F. to a temperature substantially below 1300 F. but notbelow 900 F. at the time it is coiled, each of said water quenchingtreatments being brief enough to that the outside surface of the rod isnot cooled to a temperature substantially below 900 F. before the rod iscoiled, the rate of cooling of the rod after it is coiled being reducedso that the carbide separates in the form of fine pearlite suitable forwire drawing directly without further heat treatment.

References Cited in the file of this patent UNITED STATES PATENTS2,023,285 Otis Dec. 3, 1935 2,240,019 Quarnstrom et al. Apr. 29, 19412,516,248 OBrien July 25, 1950 FOREIGN PATENTS 7 297,796 Great BritainFeb. 24, 1930 342,189 Great Britain Jan. 29, 1931

1. A METHOD OF HEAT TREATING HOT ROLLED HIGH CARBON STEEL RODS AS THEHOT ROD TRAVELS FROM THE ROLLS TO A COILING DEVICE AT A TEMPERATURE OFTHE ORDER OF 1800* F. AND AT A SPEED OF THE ORDER OF 2000 F.P.M. OR MOREWHICH COMPRISES WATER QUENCHING THE ROD AND IMMEDIATELY REMOVING SURPLUSWATER FROM THE ROD SURFACE, ALLOWING THE TEMPERATURE OF THE OUTER ANDINNER PORTIONS OF THE ROD TO EQUALIZE SUBSTANTIALLY, THEN AGAIN WATERQUENCHING THE ROD AND REMOVING SURPLUS WATER FROM THE ROD SURFACE, AGAINALLOWING THE TEMPERATURE OF THE PORTIONS OF THE ROD TO EQUALIZESUBSTANTIALLY, AND REPEATING SAID TREATMENTS SUCCESSIVELY UNTIL THEAVERAGE TEMPERATURE OF THE ROD IS REDUCED TO A TEMPERATURE OF THE ORDEROF 1100* F. AT THE TIME IT IS COILED, EACH OF SAID WATER QUENCHINGTREATMENTS BEING OF SHORT ENOUGH DURATION SO THAT THE OUTSIDE SURFACE OFTHE ROD IS NOT COOLED TO A TEMPERATURE SUBSTANTIALLY BELOW 900* F.BEFORE THE ROD IS COILED.